In a memory system using a NAND type flash memory (hereinafter, referred to as a NAND memory) as a storage medium, a threshold voltage of a memory cell changes due to, for example, data retention and read disturbance. This causes a bit error rate in the data read from the NAND memory to increase, and as a result, the reliability of the memory system may deteriorate. As a countermeasure against such a deterioration in reliability, a technique for estimating a voltage (read voltage) used at the time of reading in consideration of, for example, a change in threshold voltage or the like has been proposed.
For example, a technique of estimating the read voltage to be used for actual reading by utilizing a distribution of threshold voltages measured using a reference read voltage has been proposed. In such a technique, since the read voltage is estimated by performing a measurement using, for example, approximately seven reference read voltages, the processing time can be long. Further, in such a technique, information used for estimating the read voltage requires measuring the threshold voltage using an actual NAND memory.